1. Field of the Invention
The present invention relates generally to a scroll compressor and, more particularly, to a disposition of bypass holes and bypass passages defined in the scroll compressor and that of bypass valves mounted therein.
2. Description of Related Art
In a scroll compressor of a kind having a low vibration and a low noise emission, a suction chamber and a discharge port are defined radially outwardly of and centrally of scroll wraps forming a plurality of compression chambers therebetween, respectively, and a compression ratio determined by the volume of the suction chamber and the volume of the final compression chamber is fixed.
Particularly where variation in operating compression ratio determined by the suction pressure and the discharge pressure is small, a highly-efficient compression is possible with no need to use any discharge valve device such as employed in a reciprocating piston-type compressor or a rotary compressor for compressing a fluid medium, provided that the volume ratio of the compression chamber is determined consistently.
Where the scroll compressor is used in an air conditioner for compressing a refrigerant, the suction and discharge pressure of the refrigerant vary with changes in load on the air-conditioner and variable speed operations.
By the effect of a difference between the operating compression ratio and the preset compression ratio, the scroll compressor may suffer from insufficient compression or excessive compression. In the event of the insufficient compression, a high pressure refrigerant gas inside a discharge chamber may intermittently flow back from the discharge port into the compression chambers, accompanied by an increase of compression inputs.
Also, in the event that a liquid refrigerant or a substantial amount of lubricating oil is compressed, that is, in the event of occurrence of a so-called liquid compression phenomenon, the scroll compressor is held in a super compression condition, accompanied by not only an abnormal increase in compression inputs, but also excessive vibration to such an extent as to result in generation of noise and damage to the compressor.
In order to avoid any possible back-flow of the compressed fluid medium resulting from the insufficient compression, the use has been suggested of a check valve device 1074 such as disclosed in, for example, U.S. Pat. No. 4,650,405 and shown in FIG. 1. Referring to FIG. 1, the check valve device 1074 includes a check valve member 1076 generally in the form of a reed valve and a valve retainer 1078 both disposed in the proximity of an exit end of the discharge port 1072 defined at the center of a stationary scroll 1058.
For lessening the excessive compression, the following three bypass means are known for selectively opening and closing a communication between the compression chamber and the discharge port.
Referring to FIGS. 2, 3 and 4A-4D, there is shown the bypass means such as disclosed in Japanese Laid-open Patent Publication (unexamined) No. 3-233181. This bypass means includes a stationary scroll 1102 formed with first bypass holes 1117a and 1117b and second bypass holes 1118a and 1118b both defined therein in symmetrical relation with each other for discharging a fluid medium between two symmetrical compression chambers 1106 and an internal high pressure space within the sealed vessel 1101. The bypass means also includes a bypass valve device 1115 in the form of a reed valve for selectively opening and closing the exit end of each of the bypass holes 1117a, 1117b, 1118a and 1118b by the effect of the pressure difference.
According to the bypass means disclosed in Japanese publication No. 3-233181, when an abnormal increase in pressure occurs inside the compression chambers 1106 as a result of occurrence of the excessive compression and/or the liquid compression inside the compression chambers 1106, air being compressed can be discharged directly to the high pressure space inside the sealed vessel 1101.
As a result thereof, the pressure inside the compression chambers 1106 abruptly decreases to avoid any possible rupture of the compressor.
As shown in FIGS. 4A to 4D, the first bypass holes 1117a and 1117b and the second bypass holes 1118a and 1118b are disposed in the manner which will now be described.
When an orbiting scroll 1103 is held at an orbiting angle in which the first bypass holes 1117a and 1117b positioned radially outwardly relative to the second bypass holes 1118a and 1118b are closed by a free end face of the orbiting scroll 1103, the second bypass holes 1118a and 1118b are opened as shown in FIG. 4A. On the other hand, when the orbiting scroll 1103 is held at an orbiting angle in which the compression chamber 1106 closest to the discharge port 1128 communicates with the discharge port 1128, the second bypass holes 1118a and 1118b positioned radially inwardly relative to the first bypass holes 1117a and 1117b are closed by the free end face of the orbiting scroll 1103, as shown in FIG. 4D.
Thus, according to the arrangement shown in FIGS. 2, 3 and 4A-4D, the second bypass holes 1118a and 1118b perform no function when the compression chambers 1106 communicate with the discharge port 1128.
The other, second and third bypass means are disclosed in Japanese Laid-open Patent Publications (unexamined) No. 58-128485 and No. 63-140884, respectively.
According to the second bypass means, bypass holes are defined in communication with compression chambers which are normally closed without being communicated with any of the suction chamber and the discharge port. In this known system, the bypass holes are defined in communication with the normally closed compression chambers, because in the event of occurrence of an excessive compression within such compression chambers the compressor may be detrimentally damaged.
The third bypass means such as disclosed in Japanese publication No. 63-140884 referred to above makes use of bypass holes that are not intended to avoid the abnormal increase in pressure which would occur at the time of liquid compression. Such bypass holes are merely provided for lessening a slight excessive compression occurring during the final stage of compression when the operating compression ratio of the scroll compressor is smaller than the preset compression ratio. Accordingly, the bypass holes are defined at locations sufficient to allow the scroll compressor to exhibit a compression ratio of about 0.5 to 0.75 relative to the preset compression ratio.
However, the prior art bypass means have been found to have the following problems.
In the first place, since even when the operating compression ratio matches substantially with the preset compression ratio, the sectional area of a passage is small immediately after communication between the compression chambers and the discharge port, and an excessive compression does undesirably take place within the compression chambers after the compression.
In addition, the check valve member 1076 shown in FIG. 1 is apt not to open under the influence of an inertia force of the spring, resulting in delay in operation. As a result thereof, an excessive compression also occurs within the discharge port 1072. Specifically, during a high speed operating condition of the compressor, a considerable excessive compression takes place not only inside the compression chambers closest to the discharge port 1072, but also inside the discharge port 1072, accompanied by an increase in compression inputs. Where the operating compression ratio is lower than the preset compression ratio (that is, during the operating condition in which the excessive compression occurs), compression input losses will increase as well.
Accordingly, it is clear that the first to third bypass means discussed above, which have been tailored to minimize problems which would occur during the operating condition in which the excessive compression takes place, are ineffective to eliminate the occurrence of the excessive compression which occurs immediately after the compression chambers communicate with the discharge port.
In the second place, where in order to eliminate problems associated with the operating condition in which an insufficient compression takes place, the check valve member 1076 is employed as shown in FIG. 1 and, on the other hand, in order to eliminate problems associated with the operating condition in which the excessive compression takes place, the first to third bypass means (comprised of the bypass holes and the bypass valves), for example, are employed as discussed above, the check valve member 1076 may interfere with the plural bypass valves. For this reason, depending on the operating compression ratio and the preset compression ratio, the bypass holes cannot be defined at optimum locations, making it impossible to obtain an effective bypassing function.
It may, however, be contemplated to use inclined holes for the bypass holes so that the bypass valves can be separated from the check valve member 1076. However, this possibility requires a relatively long bypass holes which would result in an increase of the quantity of the compressed gas remaining within the compression chambers, accompanied by a reduction in compression efficiency which is brought about by reexpansion of the residual compressed gas within the compression chambers.
In the third place, the number of the bypass valves tends to be increased one for each of the bypass holes so that the bypass holes can be closed by the respective bypass valves. The use of the increased number of the bypass valves results in an increase of manufacturing cost and also generation of a considerable noise during selective opening and closing of the bypass valves to such an extent as to bring about a disadvantage to the scroll compressor known to have a low noise emission.
In addition, the necessity will arise that in order to eliminate the problem associated with interference between the check valve device and the bypass valves, the size of an effective area of each bypass valve which is used to close the corresponding bypass hole and that of the check valve device which is used to close the discharge port must be small. This may bring about such a disadvantage that a sealing function of the bypass valves relative to the bypass holes and that of the check valve device relative to the discharge port may be lowered unless the check valve device and the bypass valves are properly installed in the stationary scroll.
Finally, diffusion of the discharged gas which takes place during selective opening and closing of the check valve device tends to bring about a reduction in sealing effect of the bypass valves disposed in the proximity of the check valve device.
Because of the various reasons discussed above, it often occurs that the position of the bypass holes is determined in consideration of possible influence brought about by the check valve, making it difficult to properly position the bypass holes in a manner effective to obtain an effective bypassing function. Accordingly, little suggestion has been made to encourage the use of the bypass holes and the associated bypass valves in the scroll compressor wherein the check valve is installed for selectively closing and opening the discharge port.